Electrodeposition of metals



Patented Apr. 12, 1938 2,114,006 ELECTRODEPOSITION or METALS Virgil n. Waite, Berea, omo, .assignor to The McGean Chemical No Drawing.

1934, Serial No. plication August 5,

18 Claims.

This inventionrelates to electrodeposition of metals; and it has to do more especially with electrodeposition of metals-of the nickel group comprising nickel, cobalt and iron, employing plating baths or solutions containing an organic salt of the metal to be deposited, together with a relatively small quantity of an organic compound, particularly a sulfonic acid compound, as a catalyst, promoter, or assisting agent; the plating baths being operated relatively hot and at relatively low pH (hydrogen ion concentration); whereby electrodeposits of superior characteristics are produced. The invention comprises the novel process aforesaid, as well as the novel plating baths or solutions and the novel electrodeposits produced therefrom.

While the invention in its broader aspects is not restricted to electrodeposition of any particular metal or group of metals, but is applicable in a very wide field with varying degrees of utility, its greatest practical utility at the present time is in the electrodeposition of metals of the nickel group aforesaid, and preeminently of nickel itself. In explaining the underlying principles of the invention, therefore, reference will be made herein more particularly to nickel plating; but it will be understood that this is merely for purposes of illustration and that in its broader aspects the invention is of wider scope, as indicated.

A principal object of the invention is to produce electrodeposits of" nickel or other metal which are bright and lustrous, i. e. image-reflecting or mirror-like. In the field of decorative plating, the final bright, glossy finish usually required and sought has usually been obtained heretofore by bufling nickeled articles, which,

are then given a thin coating of chromium, for example. This sequence of operations necessitates a re-racking of the articles between the nickel and chromium plating tanks, and, what is more important, also results in a loss of nickel removed by the buffing or mechanical polishing operation, not to mention the expense of the labor involved. A method of plating whereby the nickeled articles come from the bath with a bright and lustrous finish, such as is afforded by the present invention, is therefore highly desirable.

Another object of the invention is to attain the foregoing desirable results while at the same time permitting rapid deposition of relatively thick or heavy, metal coatings as required by modern plating practice, and to do this relatively simply and economically.

With the foregoing objects in view, as well as others which will become apparent as the description proceeds, the invention consists in the novel plating processes and baths, as well as the resultant novel electrodeposits, which will Company, a corporation of Ohio Original application August 15,

740,021. Divided and this ap- 1936, Serial No. 94,437

Cleveland, Ohio,

be described in certain concrete illustrative examples hereinafter and will then be more particularly pointed out in the appended claims.

It has been proposed heretofore to produce bright or image-reflecting deposits of nickel directly in the plating bath, but all such prior proposals have involved serious disadvantages renderlng them unsuitable for economically successful application in actual practice. What little is to be found in the literature on the subject tained even experimentally. Nickel and other metal solutions are very susceptible to the action of colloids, and the amounts used, as well as other details of operation, must be carefully regulated to avoid production of cracked and curled deposits. Due either to their inherent character or to the particular manner in which it has been recommended to use them, the addition agentsheretofore suggested for use were operative only for low current densities and thin deposits and are therefore not available for use in the more recent plating practice which calls for the rapid deposition of relatively heavy coatings. Addition agents thus suggested heretofore have included a wide variety of organic compounds, as well as certain metals such as zinc or cadmium. But it has not been possible heretofore, by the use of any of those addition agents, as proposed, to obtain satisfactory bright deposits of appreciable thickness such, for example, as a thickness ofmore than 0.0002 inch; and even in the case of thinner deposits, an

approach to satisfactory brightness or lusterwas obtainable only by operating atlow current densities :impractical or very undesirable to use in modern plating practice.

According to the present invention, nickel plating baths, for example, are employed which in most respects may much resemble those now commonly used but which contain one or more addition agents which serve to promote production of bright or mirror-like deposits, which novel baths are, furthermore, operated within a temperature range above ordinary room temperature and within a pH range that is relatively low (1. e. relatively strongly acid). The particular temperature and pH vary within the indicated ranges depending .upon the particular addition agent or agents employed in any given plating bath, but may be adjusted and controlled in accordance with the present invention to give optimum results. In general the process of the invention involves operating at bath temperatures ranging from about 35 C. to about 60 C., a range of 40 to 50 C. being found especially desirable in the case of most of the addition agents most suitable for practicing the invention. The pH 9f the plating baths may range from 5.5 to 1.5, a pH of approximately 2.5 being found especially suitable in the majority of cases. Under these conditions of plating bath control or adjustment, and with the use of a proper addition agent or agents, employment of relatively high current densities in producing thoroughly satisfactory coatings becomes feasible and is also characteristic of the invention in its best embodiments. Current densities of from 30 to 50 amperes per square foot are especially suitable many cases current densities as high as 60 to 100 amperes per square foot are practical and desirable. Lower current densities, e. g. on the order of 10 amperes per square foot, are also permissible; and it is to be understood that the use of such lower current densities is within the scope of the invention in its broader aspects, although higher current densities can advantageously be employed, as above pointed out, and are preferred in practice.

In general, addition agents suitable for use in practicing the present invention comprise watersoluble organic compounds herein designated as sulfonated amino toluene compounds, including not only amino toluene (toluidine) sulfonic acids, but also suitable salts thereof and diamido dimethyl diphenyl (tolidine) sulfonic acids, as well as suitable salts thereof; compounds of this class having the amino group in the ortho position being especially suitable. It is also found that the desirable action of these agents is appreciably enhanced if they are mildly chlorinated, as, for example, by the use of a chlorine-in-water solution as the chlorinating agent. It is further found that in some cases especially good results are ob tained when a small quantity of a metal promoter, e. g. zinc or cadmium, is associated in the bath with the addition agent. The organic agents may be used singly or in combinations of two or more within the scope of the invention; but from the standpoint of simplifying control of the composition of the plating solution, it is generally more desirable to employ only one. For the same reason, it is generally better to employ only one metal addition agent or promoter (in the form of a salt) in conjunction with one organic addition agent. a

Another important feature of the invention in its best embodiments is the fact that the addition agent used is employed in only relatively very small quantity, so small indeed as not to combine with or bind chemically any substantial proportion of the amount of the plating metal present in the bath or solution to be deposited therefrom.

In other words, in the practice of this invention, the metal to be deposited ordinarily exists in the bath wholly or almost wholly as a salt of an inorganic acid; but the term inorganic acid as here used is not intended to exclude the presence in the bath of variable proportions of acetate, formate, and/or oxalate, for example, of the plating metal, which salts may be employed as buffering agents. In other words, the organic addition agents as employed in the present invention seem to function very much in the role of catalysts inpromoting the production of the superior electrodeposits obtainable in the practice and are typical, although in of the invention, said addition agents being present in relatively small and generally only minute proportion, as compared with the amount of plating metal salt or salts in the bath and apparently undergoing very little depletion in operation except for the unavoidable drag-out. In referring to the action of these addition agents as catalytic, however, it is not intended thereby in any sense to rest the present invention upon.

a theoretical basis, but only to characterize conveniently and in a general way their promoting and assisting action, in contrast to the prior proposed use, in connection with tin, copper or lead plating, of certain sulfonic acid compounds in relatively large quantities for the purpose of binding chemically approximately half or'more of the total plating metal present as a metal sulfonate. In contradistinction to methods heretofore proposed in applying the process of the invention to bright nickel plating, for example, the deposit may be made, and most desirably is made, at the relatively high temperatures and high current densities commonly employedacommercially in ordinary non-bright nickel plating practice; and the luster of the deposit becomes greater with increase of the thickness of the deposit. In fact, the present process enables plating upon a surface which is originally dull and, by continuing the deposition for a sufilcient length of time and thus obtaining a relatively thick deposit, securing a deposit that is image-reflecting or mirror-like. This remarkable result can be accomplished, moreover, by using nickel plating baths which, except for the employment of an addition agent or catalyst as herein described, have compositions otherwise usual in present commercial practice. A typical plating bath of this character may contain, for example, to 360 grams of hydrated nickel sulfate, 8 to '15 grams of nickel chloride and 8 to 45 grams of boric acid, per liter of solution.

Among the specific organic addition agents which have been found especially desirable to employ as assistants or catalysts in accordance with the invention may be mentioned the following: 2 amino toluene 5 sulfonic acid and 2 amino toluene 4 sulfonic acid (o-toluidine sulfonic acids); 4 amino toluene 2 sulfonic acid (a ptoluidine sulfonic acid) and o-tolidine disulfonic acid. The products resulting from mild chlorination of these compounds are also very effective.

A bath containing any of the materials mentioned in the next preceding paragraph produces brighter deposits if the pH is decreased (acidity increased) down to pH of 2.5 or even lower in some instances; while increase of temperature up to approximately 45 C., or in some cases higher, also causes an increase in the brightness of the deposit. Moreover, the deposits so obtained are characterized by good adherence and substantial freedom from cracking or curling, these eminently satisfactory results being obtainable over a relatively wide working range of temperature, pH value and current density, within the limits hereinabove indicated.

It is of course to be understood that, in general, salts (e. g. the sodium or other alkali metal salts, the calcium salts, etc.) of the sulfonic acids mentioned not detrimental to the plating bath may be used as addition agents or catalysts in place of the sulfonic acids themselves. Unless otherwise expressly indicated, therefore, the expression sulfonic aci is to be understood broadly to include both the free acids and salts thereof.

The amount of organic addition agent or cata- 1| lyst which is desirably employed in practicing the invention may vary, in the case of "the free sulfonic acids, for example, from 1 gram per liter up to saturation. Generally speaking, lowering the pH of the bath increases the'solubility I of the addition agents,- A

Deposits of even greater brightness are ob-' tainable when the plating solution contains not I only an organic addition agent but also a small portant feature of .the present invention. The addition to a dull nickel'plating solution-"of a) quantity of either cadmium ,orgzinc; and such conjoint use of -such m'aterials in plating "solutions, particularly in nickel plating, is an 'im-' small amount'of a solublefcompound of anas J sistantor promoter metal, e. g.-c admium o1 -.zinc, for the purpose of gettingsomebrightening ef A p and relatively thick nickel plates or. .depc'isit feet, was long ago" proposed but didnot result in production of satisfactory plating xdeposits. :As is well known, that use as heretofore proposed wastoo ineffective. and too unsafe; to be ,practicaL-especially under the operating 'condi- 1 'tions characterizing modern high-speed. plating practice;' and no way of overcoming the difliculties was known- But by employing a promoter metal in a nickel plating bath in conjunction with an organic brightening'agentin accordance with the'principles of the present invention,

7 nickelplate of any desired thickness and of 'exceptional brightness maybe easily produced,-

such deposits also "being highly satisfactory in respect to their other required properties, in-

- eluding adequate ductility and goodadherence.

The promoter-metal, which may be defined for the purposes of i this invention as a 'metalhaving the effect, when used-by itself in a'ba'thfrom which a nickel group metal is electrodeposited,

of enhancing the'brightnessof the plating metal deposited but" tending to render it brittle and non-adherent, is usually added inthe form: of the sulfate although the specific method of add.-

ing it is in general immaterial. For-example,

the metal chloride may be employed, the oxide J may be dissolved in'the acid bath,-jor the 'metal form .of its compound with" the sulfonic acid.

tobe introduced into the solution by] dissolving it from an anode. It may also be usedin the (e.' g.) used asv the principal addition agent-or catalyst. For example, excellent results are obtainable from a plating solution containing 1 one of the organic additionagents orcatalysts before mentioned together with from a trace up to about 1.6 grams of zinc per liter of solution, expressed as metal. Likewisefexcellent results are obtained by the use of cadmium as thepromoter in concentrations ranging from a trace upward to about 2.3 grams per, liter, expressed i of the resultant electrodeposits somewhat as as metal. Because these pro'm'oters} even when employed in accordance withthe present invention, have the property of reducing the ductility their concentration is increased, the concentra-" tion of either of them ina given s'olution should be adjusted in accordance with the idegreejof ductility required in the 'eleotro'deposited''metal; In order to further illustrate the principles of the invention, a few detailed examples illustrating typically goodpractice,in employing the. in I vention will now be given,.x In these e'xamples,

the plating metal to be deposited is nickel, and the composition of the bath, saveiforfithe addi tion of assisting agents in accordance' with the present invention, may be as in the ordinary and well known practice. 3 One' such; typical I bath' .composition ma'y be approximately, 32Qjgram I a in. concentration 293 grams nickel sulphate, -12 ,gra'msnickel, chlo ride and 25.5 f"grams.nicke1 acetat e 1 last mentioned compound bein :r 'for buffering eifect.

, "excellent: character are obtained Ffro'm, ,suc b fi g 12;. 3

t ni dit n a nt-aha about 24 g'ra1r1s-perliter.ofjthe-platingv solution ,(a rangesof about 9- to 24 grams .tical)., the best pH range for vbrightdeposits for a Y foot cathode current density and'a bath. tem'i practical desirable range of cathode" currenttemperature of 40 C. can'lbe takeniasapproxi mately from"30. to amperesper squar'e'footr tion otherwise similarlyconstituted, a range of Again employing the general; of. plating. bath of Example- 1," butusing 4j'aminotoluene 2" fsulfonic acid as the addition agent atan optimum to lZgrams per liter being practicahfthe best i usedas theorga'nic addition agent or catalyst at a concentration lying mostjdesirably between flabout6 andfl2 grams per liter; Within this con to 3.0, cathode current density 40- to 60 amperes j jByIincluding -in,the baths employed in-eachg liter, with boric acid present asa. bufiering agent" equal to about 31 j grams perliter. 'A bath of this general constitutionisparticularlyfsuitable'because itis a type of nickel plating solution in widespread use on account not itsdesirable characteristics when operated to produce relatively "thick deposits rapidly; In the examples given hereinafter, it will be assumed-' 1" that a bath of this.v general composition is einployed. Another typical, bath composition which may be successfully employed, however, comprises w eneop'er ii. anceiwith. the examples hereinafter-zgiv n 1: yEmqmplel I Employing 2 amino ftoluene ,5 sulfonic acid-as n e onn satisfactory character approximately 'frorri 2 '2 to-4.25, operatingat about '50 amperes per 'squar perature" of about '40-*'C. [For best results, the

density for bright depositsat pHv 2.4 and bath Example 2 a a 7 Using 2 amino'toluene 4sulfonic acid as the addition-agent, in place of the 2-5 acid employed in-Example v1, but with the plating soluf m 0to20 ramsbf eaddi-tion agent per liter works well, about '12 grams being optimumi 1 At this optimum vconcentration,1 the best work-' ing conditions. are as 'follows (approximately) pH 2.0 m) 50,- cathode current densityq-2oto 5o 45 d amperes per square foot, .2 and]terr p'erature 40'? concentration are-grams perliter (a range of 4 foot and bath-temperature of 40 C.', is approximately 2.5 1505.2. At pH 12.5, and bath temperature' 40- C., -the mostfdesirable practical range} for bright deposits may betaken as approximate-' ly from 30 to 75 amperes persquare' foot.

i .Ercmplesllf "In this case, .ortho-t'olidi'ne disulfoniclacid is ples a promoterfin,etal in 7 the form of a soluble salt thereof, in addition to the organic addition agent, the resultant plates or deposits are noticeably brighter and also satisfactory in other respects. When employing cadmium as the promoter metal, particularly good results are obtained at a concentra-' tion in the neighborhood of 0.2 gram per liter expressed in terms of the metal. When zinc is employed as the promoter, concentrations up to about 1 gram per liter are found to be very satisfactory. Increase of the zinc concentration to as high as 3 grams per liter tends to cause brittleness in the deposit, and any addition of zinc as a promoter should therefore desirably be kept safely below this concentration for best results. This tendency to cause brittleness is less marked in the case of zinc, however, than in the case of cadmium. The promoter metal may be conveniently added in the form of a soluble salt, such as the sulfate or chloride. In general, with lower concentrations of the plating metal in the bath, the concentration of the promoter metal should also be lower, although not necessarily proportionately lower. In general, the concentration of the promoter metal dissolved in the bath should not substantially exceed one-tenth normal In the foregoing examples, the concentration of the plating metal in the bath is specified as approximately 2.5 N in each instance as illustrative of typical good practice, and the amounts of the various addition agents or catalysts specified are generally indicative of satisfactory concentrations thereof in such plating baths. It is to be understood, however, that considerable variation from these optimum concentrations and other operating conditions is permissible within the scope of the invention in its broader aspects.

It is found that during the plating operation the addition agents or catalysts and/or promoters may in some cases become concentrated at the surfaces of the cathodes or work being plated. When the work is removed from the bath and rinsed, therefore, such addition agents are removed from the solution at a more rapid rate, relatively, than are the other constituents of the plating bath. Accordingly, in order to compensate for the drag-out in the maintenance of the bath in such cases, it is necessary to add relatively larger proportions, of the catalyst and promoter in respect to the other materials,

than are used in making up a new solution or bath. The correct proportions may be found by chemical analysis or other suitable tests, and will vary with the amount of solution drag-out per ampere hour of plating.

The plating baths containing the addition agents or catalysts herein referred to have bet ter throwing power than the same solutions not containing them; that is, such baths produce upon an irregularly shaped article a plate of more nearly uniform thickness than do baths not containing them.

The use of the organic compounds hereinabove specifically named, as addition agents in plating baths, is believed to be broadly novel irrespective of the quantity or concentration thereof in such baths or of the other plating conditions under which such baths are employed.

The deposits obtained when using a promoter metal in conjunction with a sulfonic addition agent or "catalyst as in Example hereinabove, are found upon analysis to contain in the neighborhood of 0.08 per cent carbon and 0.04 per cent sulphur, together with a larger percentage of the promoter metal. In typical instances, where zinc is used as the promoter, the percentage thereof in the deposit may be about 4.3, and where cadmium is the promoter, the percentage thereof may be around 0.8.

This application is a division of my prior copending application Serial No. 740,021, filed August 15, 1934.

What is claimed is:

1. The process of producing bright or mirrorlike deposits of nickel which comprises electrodepositing nickel from an aqueous acid bath containing it mainly in the form of an inorganic salt, with the aid of a brightener comprising a toluidine sulfonic acid in quantity too small to bind chemically more than a small proportion of the nickel present in the bath.

2. The process of producing bright or mirrorlike deposits of nickel which comprises electrodepositing nickel from an equeous acid bath containing it mainly in the form of an inorganic salt, with the aid of a brightener comprising an ortho toluidine sulfonic acid in quantity too small to bind chemically more than a small proportion of the nickel present in the bath.

3. The process of producing bright or mirrorlike deposits of nickel which comprises electrodepositing nickel from an aqueous acid bath containing it mainly in the form of an inorganic salt, with the aid of a brightener comprising a tolidine sulfonic acid in quantity too small to bind chemically more than a small proportion of the nickel present in the bath.

4. The process of producing bright or mirrorlike deposits of nickel which comprises electrodepositing nickel from an aqueous acid bath containing it mainly in the form of an inorganic salt, with the aid of a brightener comprising an ortho tolidine sulfonic acid in quantity too small to bind chemically more than a small proportion of the nickel present in'the bath.

5. The process of producing bright or mirrorlike deposits of a nickel group metal which comprises electrodepositing such metal from an aqueous acid bath containing the same mainly in the form of an inorganic salt, with the aid of a brightener selected from the group'consisting of the following: 2 amino toluene 4 sulfonic acid, 2 amino toluene 5 sulfonic acid, 4 amino toluene 2 sulfonic acid, o-tolidine disulfonic acid, products resulting from mild chlorination thereof, and salts of the foregoing, the quantity of such brightener employed being too small to bind chemically more than a small proportion of the nickel group metal present in the bath.

6. The process of producing bright or mirrorlike deposits of nickel which comprises electrodepositing nickel from an aqueous acid bath containing the same mainly in the form of an inorganic salt, with the aid of a brightener selected from the group consisting of the following: 2 amino toluene 4 sulfonic acid, 2 amino toluene 5 sulfonic acid, 4 amino toluene 2 sulfonic acid, oetolidine disulfonic acid, products resulting from mild chlorination thereof, and salts of the foregoing, the quantity of such brightener employed being too small to bind chemically more than a small proportion of the nickel present in the bath.

'7. The process of producing bright or mirrorlike deposits of nickel of substantial thickness (1.

e. more than 0.0002 inch) and characterized by 2,114,006 good adherence and substantial freedom from cracking or curling, which comprises electrodepositing nickel from an equeous acid bath containing the same mainly in the form of an inorganic salt, with the aid of a brightener comprising a water-soluble sulfonated amino toluene compound employed in quantity too small to bind chemically more than a small proportion of the nickel present in the bath, and a promoter metal, employed at a concentration not substantially exceeding one-tenth normal 10 cooperating with said brightener to enhance the brightening eflect.

8. The process defined in claim 1, further characterized by the fact that said bath contains a promoter metal, employed at a concentration not substantially exceeding one-tenth normal cooperating with said brightener to enhance the brightening effect.

9. The process defined in claim 3, further characterized by the fact that said bath contains a promoter metal, employed at a concentration not substantially exceeding one-tenth normal cooperating with said brightener to enhance the brightening effect.

10. The process of producing bright ormirrorlike nickel plating of substantial thickness (1. e. more than 0.0002 inch) and characterized by good adherence and substantial freedom from cracking or curling, which comprises electrodepositing nickel from an acidic aqueous plating bath containing it in the form of an inorganic salt, together with a brlghtener selected from the group consisting of the following: 2 amino toluene 4 sulfonic acid, 2 amino toluene 5 sulfonic acid, 4 amino toluene 2 sulfonic acid, o-tolidine disulfonic acid, products resulting from mild chlorination thereof, and salts of the foregoing, the quantity of such brightener employed being too small to bind chemically more than a small proportion of the nickel group metal present in the bath; and a promoter metal cooperating. therewith to enhance the brightening-effect and employed at a concentration not substantially exceeding onetenth normal 11. The process defined in claim 10, further characterized by the fact that the promoter metal is selected from the group consisting of cadmium and zinc.

12. The process defined in claim 5, wherein the plating bath is maintained at a temperature between and 60 (3., most desirably between 40 and 50 C., and at a pH between 5.5 and 1.5,

most ,desirably at about 2.5, and is operated at a.

cathode current density of between 10 and 100 amperes, most desirably between 30 and 50 amperes, per square foot.

13. The process defined in claim 6. wherein the plating bath is maintained at a temperature between 35 and 60 0., most desirably between 40 and 50 0., and at a pH between 5.5 and 1.5, most desirably at about 2.5, and is operated at a cathode current density of between 10 and 100 amperes, most desirably between 30 and 50 amperes, per square foot.

14. An electroplating bath for producing a bright deposit of a nickel group metal which comprises an acidic aqueous solution of a compound of a nickel group metal, together with a brightener selected from the group consisting of the following: 2 amino toluene 4 sulfonic acid, 2 amino toluene 5 sulfonic acid, 4 amino toluene 2 sulfonic acid, o-tolidine disulfonic acid, products resulting from mild chlorination thereof, and salts of the foregoing, the quantity of such brightener employed being too small to bind chemically more than a small proportion of the nickel group metal present in the bath.

15. An electroplating bath for producing a A 16. An electroplating bath for producing bright nickel plating of substantial thickness (i. e. more than 0.0002 inch) and characterized by good adherence and substantial freedom from cracking or curling, which comprises an aqueous solution containing nickel mainly in the form of an inorganic salt, together with a sulfonated amino toluene compound brightening agent in quantity too small to bind chemically more than a small proportion of the nickel present in the bath, and a promoter metal adapted to cooperate with said sulfonated compound to enhance the brightening effect and employed at a concentration not substantially exceeding one-tenth normal said bath having a pH value of between 1.5 and 5.5.

1'7. An electroplating bath for producing bright nickel plating of substantial thickness (1. e. more than 0.0002 inch) and characterized by good adherence and substantial freedom from cracking or curling, which comprises an aqueous solution having an acid reaction and containing nickel mainly in the form of an inorganic salt, together with an organic brightener selected from the group consisting of the following: 2 amino toluene 4 sulfonic acid, 2 amino toluene 5 sulfonic acid, 4 amino toluene 2 sulfonic acid, q-tolidine disulfonic acid, products resulting from mild chlorination thereof, and salts of the foregoing, the quantity of such brightener employed being too small to bind chemically more than a small proportion of the nickel group metal present in the bath; together'with a promotor metal adapted to cooperate with said sulfonated compound to enhance the brightening effect and employed at a concentration not substantially exceeding onete th I n normg al 18. An electroplating bath as defined in claim #17,. wherein the promoter metal is selected from the group consisting of cadmium and zinc. VIBGIL H. WAITE. 

